The invention relates to methods for ultrasonic noise reduction in titanium-containing materials. In particular, the invention relates to methods for ultrasonic noise reduction in titanium alloy forgings.
Nondestructive evaluation by ultrasonic inspection and ultrasonic inspection testing is a known material testing and evaluation method. Ultrasonic testing typically requires that items to be detected possess high acoustic reflectance behaviors from bulk material under ultrasonic inspection. This different behavior permits the ultrasonic inspection technique to detect flaws, large and/or abnormal grains, imperfections, and other related microstructural characteristics for a material.
Materials with large, elastically anisotropic grains, such as, but not limited to, cast ingots of steels, titanium alloys, and nickel alloys, are often difficult to evaluate by ultrasonic testing. The difficulties arise, at least in part to, because sound waves, which are used for ultrasonic inspection, can be partially reflected from grains, and represent a background xe2x80x9cnoise.xe2x80x9d The generated background noise can mask flaws in the material, and is thus undesirable.
Ultrasonic inspection techniques have been developed that use focused ultrasonic beams to enhance a flaw fraction within any instantaneously insonified volume of material. These developed ultrasonic inspection techniques can identify indications based both on maximum signal, as well as signal to noise. The scattering of sound in a polycrystalline metallic material body, which is also known in the art as attenuation of a propagating sound wave, can be described as a function of at least one of the following: grain dimensions, intrinsic material characteristics, and ultrasound frequency. Typically, three different functional relationships among scattering, frequency, and grain dimensions have been described. These are:
for xcex greater than 2 xcfx80D, a=Tv4"THgr", termed xe2x80x9cRayleighxe2x80x9d scattering;
for xcex less than 2 xcfx80D or xcex≅D, a=Dv2xcexa3, termed xe2x80x9cstochasticxe2x80x9d or xe2x80x9cphasexe2x80x9d scattering; and
for xcex less than  less than D, axe2x88x9d1/D, termed xe2x80x9cdiffusionxe2x80x9d scattering;
where a is the attenuation, xcex is the wavelength of the ultrasound energy, v is the frequency of the ultrasound energy, D is an average grain diameter, T is a scattering volume of grains, and "THgr" and xcexa3 are scattering factors based on elastic properties of the material being inspected.
The microstructure of a material can determine the applications in which the material can be used, and the microstructure of a material can limit the applications in which the material can be used. The microstructure can be evaluated by measuring the scattering of sound waves in a material. The scattering of sound in a material, such as titanium, is sensitive to its microstructure. The titanium microstructure""s sound scattering sensitivity can be attributed to xcex1Ti particles that are arranged into xe2x80x9ccolonies.xe2x80x9d These colonies typically have a common crystallographic (and elastic) orientation, and these colonies of xcex1Ti particles can behave as large grains in the titanium material. An individual xcex1Ti particle might be about 5 xcexcm in diameter, however, a colony of xcex1Ti particles could be greater than about 200 xcexcm in diameter. Thus, the size contribution attributed to sound scattering sensitivity from xcex1Ti particles could vary over 40-fold among differing microstructures. Additionally, the sound scattering sensitivity due to xcex1Ti particles could change between that from randomly oriented xcex1Ti particles to that from xcex1Ti particles within oriented colonies of xcex1Ti particles.
Colony structures are formed during cooling a titanium alloy from a high temperature as xcex2Ti transforms to xcex1Ti. There is a crystallographic relation between the xcex1Ti and the parent xcex2Ti grain, such that there are only three crystallographic orientations that xcex1Ti will take when forming from a given xcex2Ti grain. If the cooling rate is high and there is uniform nucleation of xcex1Ti throughout the grain, neighboring xcex1Ti particles have different crystallographic orientations, and each behave as distinct acoustic scattering entities. However, if there are only a few sites of xcex1Ti nucleation within the xcex2Ti grain, then the xcex1Ti particles in a given area all grow with the same crystallographic orientation, and a colony structure results. This colony becomes the acoustic entity. Since a colony is formed within a xcex2Ti grain, the colony size will be no larger than the xcex2Ti grain size. The size of xcex2Ti grains and the nature of xcex1Ti particles colony structures are important variables that influence ultrasonic noise and ultrasonic inspection in single phase and two-phase titanium alloys and materials. Therefore, the size of xcex2Ti grains and the nature of xcex1Ti particles in colony structures may influence ultrasonic inspection techniques, methods, and results by creating undesirable noise during ultrasonic inspection. While thermomechanical processing techniques, which rely on dynamic recrystallization in at least one of the xcex2 and the xcex1+xcex2 temperature ranges to achieve uniform fine grain (UFG) xcex1Ti particles and prevent colony formation, have been developed to improve titanium microstructure, defects may remain in the titanium material. These defects may be undesirable for some titanium material applications, particularly those that are fatigue-life limiting applications.
There are a number of patents directed to ultrasonic inspection titanium alloys. For example, U.S. Pat. No. 5,631,424, entitled xe2x80x9cMethod For Ultrasonic Evaluation Of Materials Using Time Of Flight Measurementsxe2x80x9d issued to Nieters et al, and U.S. Pat. No. 5,533,401, entitled xe2x80x9cMultizone Ultrasonic Inspection Method And Apparatusxe2x80x9d issued to Gilmore, and assigned to General Electric, the entire contents of which are fully incorporated by reference herein. The ultrasonic inspection results for titanium, as described in these patents, may be dependent on the processing of the titanium and its structural configurations. Various processing methods for titanium and some structural configurations may result in generated noise during ultrasonic inspection, such as, but not limited to, generated high-ultrasonic noise, and may not provide desirable ultrasonic inspection results.
The high-ultrasonic noise that is generated during ultrasonic inspection of titanium-containing articles is undesirable. The generated noise can present problems in determining acceptable titanium microstructures, as the noise can lead to at least one of, but not limited to, a reduced possibility of detecting defects, increased ultrasonic inspection times, increased part inventory, and, possibly titanium parts needing to be scrapped because they can not be accurately inspected.
Therefore, a need exists for titanium processing and formation methods that can provide ultrasonic inspection of the formed titanium with reduced noise. Further, a need exists for titanium processing and formation methods that provide enhanced ultrasonic inspection of the formed titanium, in which the titanium comprises large diameter articles, such as titanium forgings.
Accordingly, a method is set forth for processing titanium into a titanium article, in which the titanium exhibits enhanced ultrasonic inspection characterization for determining its acceptability in microstructurally sensitive titanium applications. The method for processing titanium comprises providing titanium at a temperature above its xcex2-transus temperature; quenching the titanium from a temperature above the xcex2-transus temperature, the step of quenching titanium forming fine grain xcex1-plate microstructure in the titanium; and deforming the quenched titanium into a titanium article, the step of deforming the quenched titanium transforming the xcex1-plate microstructure into discontinuous-randomly textured xcex1 particles. The discontinuous-randomly textured cc particles lead to a reduction in ultrasonic noise during ultrasonic inspection.
In another aspect of the invention, a method for processing titanium into a titanium article is provided. The method provides titanium that exhibits enhanced ultrasonic inspection results for determining its acceptability in microstructurally sensitive titanium applications. The method for processing titanium comprises providing titanium at a temperature above its xcex2-transus temperature; quenching the titanium from a temperature above the xcex2-transus temperature, in which the step of quenching titanium forming fine grain xcex1-plate microstructure in the titanium without colonies; and deforming the quenched titanium into a titanium article by applying a compressive strain to the water-quenched titanium, the step of applying a compressive strain transforming the xcex1-plate microstructure into discontinuous-randomly textured xcex1 particles. The discontinuous-randomly textured xcex1 particles lead to a reduction in ultrasonic noise during ultrasonic inspection, the discontinuous-randomly textured xcex1 particles comprise grains sizes less than about 10 xcexcm, and the method reduces defects in the titanium microstructure following the step of deforming.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.